1. Field of Invention
This invention relates to the field of solvent soluble polymers which are photo-sensitive or radiation sensitive and provide solvent insoluble products with utility in making resist imaging materials and other image forming materials.
2. Background Art
Compounds containing conjugated acetylenic bonds in a linear chain are well known in the art. These compounds are variously referred to as polyacetylenic compounds and polyynes. Their preparation is disclosed in U.S. Pat. No. 2,816,149, U.S. Pat. No. 2,941,010, and U.S. Pat No. 3,065,283 and variations are disclosed in later patents.
The fact that polyynes as a class contain many radiation sensitive compounds is also well known in the art (U.S. Pat. No. 3,502,297; U.S. Pat. No. 3,501,301; U.S. Pat. No. 3,501,303; U.S. Pat. No. 3,501,308). These references emphasize the crystalline nature of the materials and the fact that they give colored results on radiation exposure. They also disclose their use in imaging as microcrystals dispersed in a binder.
In addition to radiation sensitive polyynes, some polymers are thermochromic (U.S. Pat. No. 3,723,121; U.S. Pat. No. 4,215,208; U.S. Pat. No. 4,452,995), others are radiation sensitive only under the influence of an electric field (U.S. Pat. No. 3,726,769), and yet others are electrosensitive when coated as a layer on the surface of certain photoconductors (U.S. Pat. No. 3,772,011).
Increased radiation sensitivity is disclosed for certain explicit polyynes e.g. amine salts of carboxylated polyynes in U.S. Pat. No. 3,743,505 and its divisional cases U.S. Pat. No. 3,844,791, U.S. Pat. No. 3,954,816 and U.S. Pat. No. 4,066,676. Most radiation sensitive polyynes respond primarly to UV rays and to electron beams.
The radiation sensitivity of many polyynes may be enhanced and extended to wavelengths other than those of their fundamental sensitivity by the addition of spectral sensitizing compounds to the sensitive composition. Thus sensitivity to visible light is conferred by inorganic metallic salts (U.S. Pat. No. 3,772,027; U.S. Pat. No. 3,822,134) and by pyrylium, thiapyrylium, and selenopyrylium salts (U.S. Pat. No. 3,772,028). Sensitivity to X-rays is conferred by organometallic compounds such as triphenylbismuthine and hexaphenyldilead (U.S. Pat. No. 3,811,895).
Enhancement of the primary produced image (by radiation or heat) can be accomplished by subsequent uniform illumination to wavelengths absorbed by the colored imaged (U.S. Pat. No. 3,794,491) or by subsequent heating (U.S. Pat. No. 3,501,302).
The mechanism by which polyynes (that is, inclusive of diynes upward) produce colored results under the action of radiation or heat has also been studied in the literature. (Contemporary Topics in Polymer Science Vol. 2 Pages 190-194 Edited by E. M. Pearce and J. R. Schaefgen, Plenum Press New York & London 1977; G. Wegner, Pure & Appl. Chem. 49 443-454 (1977)). This work has shown that the effect is a radiation induced polymerization in which the .alpha.-carbons of the end acetylene groups of the polyyne react by addition to form a fully conjugated linear chain. The reaction is reported to occur only in the solid state. The making of such polymers in liquid phases rather than in the solid phase is claimed in several patents (U.S. Pat. No. 4,220,747; CA Pat. No. 1,043,945) and the change in solubility from polyyne to polymerized polyyne is noted. This change in solubility is applied to photoresist systems for printing plates and high resolution electronic circuit making in U.S. Pat. No. 3,836,709 and U.S. Pat. No. 4,439,514.
Use of the polyyne polymers per se is disclosed for reversible thermochromic imaging (U.S. Pat. No. 4,215,208; U.S. Pat. No. 4,452,9959) and for non-linear optical materials (U.S. Pat. No. 4,431,268).
To summarize the art described so far, the polyyne chains are disclosed as radiation sensitive in the solid state to give colored polymers by addition reaction of the end acetylene groups. These polymers may be relatively insoluble compared with the polyynes, and may show thermochromic, or non-linear optical properties. None of the disclosures indicates that these polymerized polyynes remain radiation sensitive in the more direct sense except to the extent that feeble images may be amplified by further non-imagewise illumination.
In many of the above disclosures it is emphasized that not only is the polyyne itself crystalline but the resulting colored polymer is also crystalline and of high strength, or at least has two-dimensional periodicity as in nematic liquid crystals (U.S. Pat. No. 4,220,747; U.S. Pat. No. 4,431,263). Furthermore in U.S. Pat. No. 4,439,514 it is disclosed that when a crystalline array of diynes is very regular, polymerization across a pair of adjacent acetylene bonds by one absorbed photon initiates progressive polymerization along a line of adjacent diyne molecules. Thus high quantum efficiencies are found in such systems, with values between 10.sup.8 and 10.sup.12 molecules reacted per absorbed photon. This same patent discloses that to maintain high quality imaging properties under these conditions, heat treatement of the coated layer of diynes is used to create micro-crystalline domains, the boundries between which obstruct polymerization across them. The polymerized forms are not only colored but are not easily soluble in solvents.
Copolymers of diynes with other organic comonomers are known in the art, in which the acetylene bonds are not used in the polymerization. Thus A. S. Hay in U.S. Pat. No. 3,300,456, U.S. Pat. No. 3,594,175 and J. Polym. Sci. A-1, 8.1022 (1970) describes polymers of the form EQU H--C.tbd.C--CH.sub.2 O--.sub.m R--CH.sub.2 O--.sub.n C.tbd.C].sub.p H
wherein m and n are independently 0 or 1, p is at least 10 and R is an arylene or alkylene radical or a combination of these radicals, or a combination of two arylene or alkylene radicals with a intermediate carbonyl, or sulfone group. Certain of these copolymers are soluble in solvents and can be coated as layers on a substrate. Their initial amorphous form can be changed to crystalline by washing with certain solvents. In the later patent these polymers are described as being capable of crosslinking under the influence of radiation, but this is accomplished only with some difficulty. Inclusion of sensitizing compounds such as rose bengal, tetraiodofluorescein, hemoporphyrin, and p-diethynylbenzene can give crosslinking with much less radiation. The crosslinked forms are not easily soluble in solvents and the polymers may therefore be used as photoresists.
Further copolymers of diynes with other comonomers such as urethane, ester, amide, and urea groups are disclosed by Fischer & Wegner in U.S. Pat. No. 3,709,860 and by G. Wegner in Makrom. Chem. 134, 219 (1970). These polymers contain diyne units EQU --O--CHR.sup.1 --C.tbd.C--C.tbd.C--CHR.sup.2 --O--
interspersed with hydrocarbon, polyether and urethane etc. units. Suitable polymers contain at least 20% by weight of the diyne units above and contain groups capable of forming secondary valence bonds and contain crystalline fractions. The polymers are soluble in solvents but on exposure to radiation become colored and insoluble, thus being suitable for photoresist imaging systems. Examples indicate exposures required are 5-20 minutes to a powerful ultraviolet lamp. It is indicated that non-diyne units as well as the diyne units respond to the radiation. Photosensitizers known in the art may be used.
Patil et al in J. Polym. Sci., Polym. Chem. Ed. 19.115 (1981) discloses the preparation and properties of a series of aliphatic and aromatic polyesters containing a diacetylene unit in the backbone of their repeating unit.
Hanson in U.S. Pat. No. 4,439,590 discloses polymers of the form ##STR1## wherein R is a strong electron withdrawing group like ##STR2## or --CO--. These polymers are not disclosed as radiation sensitive and do not contain the conjugated diacetylenes.
Thus, early workers on the polymerization of diacetylene monomers found that diacetylenes in the crystalline state polymerize efficiently on exposure to light or heat. Wegner, Hay and Patil have incorporated the diacetylene functionality into polymers such as polyesters, polyurethanes and polyphenyl ethers. These polymers in general have a large number of repeat units in the crystalline segment. Crosslinks in the crystalline segments of these polymers connect the same chains and will therefore be effectively redundant, thereby leading to lower photographic efficiency. It is an aspect of this invention to improve the photosensitivity of the diacetylene functionality by increasing the degree of crystallinity while keeping the number of repeat units in the crystalline segments to a minimum.